Cyperus

Illustrator: Yevonn Wilson-Ramsey

Copyright: Flora of North America Association

Herbs, perennial or less often annual, cespitose or not, rhizomatous, stoloniferous, rarely tuberous. Culms solitary or not, trigonous or round, glabrous or scabridulous with extrorse or antrorse (rarely retrorse) prickles. Leaves usually basal; ligules absent; blades keeled abaxially, flat, V-, or inversely W-shaped in cross section. Inflorescences terminal, rarely pseudolateral, 1st order subumbellate to capitate, 2d order with spicate or digitately arranged spikelets, rarely a solitary spikelet; spikelets 1–150; 1st order rays unequal (rarely equal) in length, produced singly from the axils of inflorescence bracts; involucral bracts 1–22, spirally arranged at culm apex, spreading to erect, leaflike. Spikelets: scales to 76, distichous, each subtending flower, cylindric to compressed, borne spicately or digitately at ends of rays (occasionally proliferous). Flowers bisexual [rarely unisexual], in axils of distichous floral scales, bases often decurrent onto rachilla as ± hyaline wings; perianth absent; stamens 1–3; styles linear, 2–3-fid, base deciduous or persistent; stigmas 2–3. Achenes biconvex, flattened, or trigonous.

Distribution

Pantemperate and tropical.

Discussion

Species ca. 600 (96 in the flora).

Selected References

Carter, J. R. 1984. A Systematic Study of the New World Species of Section Umbellati of Cyperus. Ph.D. dissertation. Vanderbilt University.

Corcoran, M. L. 1941. A revision of the subgenus Pycreus in North and South America. Catholic Univ. Amer., Biol. Ser. 37: 1–68.

Denton, M. F. 1978b. The Luzulae group of Cyperus (Cyperaceae). Contr. Univ. Michigan Herb. 11: 197–271.

Horvat, M. L. 1941. A revision of the subgenus Mariscus found in the United States. Catholic Univ. Amer., Biol. Ser. 33: 1–147.

Marcks, B. G. 1972. Population Studies of North American Cyperus Section Laxiglumi (Cyperaceae). Ph.D. dissertation. University of Wisconsin.

Marcks, B. G. 1974. Preliminary reports on the flora of Wisconsin, no. 66. Cyperaceae II—Sedge family II. The genus Cyperus—the umbrella sedges. Trans. Wisconsin Acad. Sci. 62: 261–284.

McGivney, M. V. 1938. A revision of the subgenus Eucyperus found in the United States. Catholic Univ. Amer., Biol. Ser. 26: 1–74.

Tucker, G. C. 1983. The taxonomy of Cyperus (Cyperaceae) in Costa Rica and Panama. Syst. Bot. Mongr. 2: 1–85.

Tucker, G. C. and R. McVaugh. 1993. Cyperus. In: R. McVaugh and W. R. Anderson, eds. 1974+. Flora Novo-Galiciana: A Descriptive Account of the Vascular Plants of Western Mexico. 8+ vols. Ann Arbor. Vol. 13, pp. 270–344.

Tucker, G. C. 1994. A revision of the Mexican species of Cyperus L. (Cyperaceae). Syst. Bot. Monogr. 43: 1–214.

Lower Taxa

Cyperus subg. Cyperus, Cyperus subg. Diclidium, Cyperus subg. Juncellus, Cyperus subg. Pycnostachys, Cyperus subg. Pycreus

Keys

Key to Subgenera

1	Stigmas 2 (3 in C. serotinus); achenes biconvex.	> 2
1	Stigmas 3; achenes trigonous, plano-convex, or terete.	> 3
2	Achenes laterally flattened, borne with edge toward rachilla.	Cyperus subg. Pycreus
2	Achenes dorsiventrally flattened, borne with face toward rachilla.	Cyperus subg. Juncellus
3	Spikelets borne in digitate clusters (rarely singly) or in umbellate or glomerulate heads.	Cyperus subg. Pycnostachys
3	Spikelets borne in spikes on conspicuous rachis.	> 4
4	Rachilla continuous or articulate only at base.	Cyperus subg. Cyperus
4	Rachilla articulate at base of each scale, mature spikelet disarticulating into segments consisting of scale, internode, and rachilla wings.	Cyperus subg. Diclidium

Artificial key to species

1	Stigmas 2; achenes biconvex to flattened, subcylindric, or cylindric	> 2
1	Stigmas 3; achenes usually trigonous	> 15
2	Achenes dorsiventrally flattened, borne with face toward rachilla	> 3
2	Achenes laterally flattened, biconvex, or subcylindric, borne with edge toward rachilla	> 5
3	Rays absent or sometimes 1, at most 2 mm; inflorescence capitate, appearing lateral; longest inflorescence bract erect, like continuation of culm	Cyperus laevigatus
3	Rays 2–26; inflorescence spicate, not appearing lateral; longest inflorescence bracts horizontal to ascending at 45°	> 4
4	Inflorescence bracts 5–25 cm; culms 50–100 cm; spikes ovoid; achenes 1.4–1.6 mm	Cyperus serotinus
4	Inflorescence bracts 20–100 cm; culms 150–250 cm; spikes cylindric; achenes 0.9 mm	Cyperus alopecuroides
5	Apex of floral scales with excurved awn 0.3–0.5 mm; stamens 1–2; achenes 0.6 mm; Florida	Cyperus pumilus
5	Apex of floral scales with or without mucro; stamens 2–3; achenes (0.7–)1–1.6 mm; widespread	> 6
6	Achenes oblong with truncate apex, subcylindric, not much laterally compressed to biconvex or ± cylindric	> 7
6	Achenes ovoid, obovoid, or ellipsoid with rounded or subacute apex, laterally flattened or biconvex	> 9
7	Anthers 0. 1–0.2 mm; styles 0.1–0.3(–0.4) mm; stigmas 0.3–0.4 m	Cyperus fugax
7	Anthers (0.4–)0.5–0.8 mm; styles 0.6–2.1 mm; stigmas 1–2 mm	> 8
8	Floral scales 1.5–2.4 × 1–1.4 mm; achenes 0.8–1.2 × 0.4–0.6 mm	Cyperus polystachyos
8	Floral scales 2.7–3.6 × 1.6–1.8 mm; achenes 1.2–1.6 × 0.6–0.9 mm	Cyperus filicinus
9	Plants annual; culms 30–75 cm; floral scales with conspicuous clear border, ovate, loosely imbricate, each barely overlapping next, spikelet margins appearing serrate	Cyperus flavicomus
9	Plants perennial or annual; culms 4–40(–95) cm; floral scales without clear border, oblong, closely imbricate, spikelet margins appearing entire	> 10
10	Surface of achenes with network of ridges forming rectangular, longitudinally elongate cells and transverse undulations; achenes broadly obovoid, black or reddish brown; stamens 3	Cyperus flavescens
10	Surface of achene with network of ridges forming isodiametric or square cells, without transverse undulations; achenes ellipsoid or obovoid, brown or black; stamens 2 or 3	> 11
11	Floral scales yellow or yellowish brown, never purple or purple-tinged	Cyperus lanceolatus
11	Floral scales brown to nearly black or castaneous, sometimes hyaline or yellow, then purple-tinged	> 12
12	Plants perennial with slender rhizomes; floral scales castaneous, blackish or occasionally light brown; achenes ovoid to ellipsoid	> 13
12	Plants annual with fibrous roots; floral scales brown (rarely yellow or stramineous) or reddish brown; achenes obovoid to ovoid	> 14
13	Achenes 1.2–1.4 mm; anthers 0.6–0.8 mm; Oklahoma to Oregon, southward	Cyperus melanostachyus
13	Achenes 1–1.4 mm; anthers 0.3–0.6 mm; Alabama, Georgia, Louisiana, Mississippi	Cyperus sanguinolentus
14	Floral scales 1.9–2.7 × 1.8–2.3 mm; styles 0.6–1 mm; stigmas 1–1.5 mm	Cyperus bipartitus
14	Floral scales 2.5-3 × 1.6–1.9 mm; styles 0.3–0.5 mm; stigmas 2.2–3.1 mm	Cyperus diandrus
15	Spikelets in digitate clusters (rarely solitary), or in umbellate or glomerulate heads	> 16
15	Spikelets in spikes on conspicuous rachis	> 49
16	Floral scales 2-keeled in proximal 30–60%	> 17
16	Floral scales not 2-keeled, conduplicate (or broadly rounded)	> 28
17	Leaves without blades; inflorescence bracts ca. 20, all ± horizontal; stamens 3	Cyperus involucratus
17	Leaves with blades; inflorescence bracts 2–10(–40), at various angles; stamens 1 (rarely 2)	> 18
18	Culms trigonous, harshly scabrid on angles only; leaf blades and bracts with conspicuous cross ribs	> 19
18	Culms trigonous, subterete, or terete, glabrous or scabridulous; leaf blades and bracts without cross ribs	> 20
19	Rays 6–12; floral scales oblanceolate, (1.3–)1.5–2(–2.4) mm; achenes 1.2–1.5 mm	Cyperus virens
19	Rays 3–5; floral scales ovate, 1.4–1.6 mm; achenes 1–1.2 mm	Cyperus drummondii
20	Culms scabridulous with retrorse prickles	Cyperus surinamensis
20	Culms glabrous or with antrorse or extrorse prickles	> 21
21	Achenes with swollen, spongy base	Cyperus distinctus
21	Achenes without swollen, spongy base	> 22
22	Achenes broadly ellipsoid, stipitate or cuneate	> 23
22	Achenes narrowly ellipsoid to linear, not or barely stipitate	> 25
23	Plants annual; longest inflorescence bract erect to ascending; anther 0.5 mm; widespread	Cyperus acuminatus
23	Plants perennial; longest inflorescence bract horizontal to ascending at 30°; anther 0.8–1.2 mm; Gulf or Pacific coasts	> 24
24	Floral scales 2–2.3 mm, declined 30–45° from rachilla; achenes stipitate	Cyperus eragrostis
24	Floral scales (1.2–)1.5–2 mm, declined (45–)60–90° from rachilla; achenes cuneate to stipitate	Cyperus ochraceus
25	Longest bract erect, appearing as continuation of culm; spikelets reddish	Cyperus reflexus
25	Longest bract (horizontal-)ascending at 30–60(–75)°; spikelets greenish white	> 26
26	Achenes linear (slightly curved); spikelets ovoid	Cyperus pseudovegetus
26	Achenes ellipsoid to narrowly ellipsoid; spikelets linear to broadly ellipsoid	> 27
27	Floral scales 1–1.5 mm; bracts horizontal to ascending at 30°	Cyperus surinamensis
27	Floral scales (1.2–)1.4–1.6(–1.8) mm; bracts ascending at 45–60(–75)°	Cyperus entrerianus
28	Plants annual	> 29
28	Plants perennial (C. gracilis annual or perennial)	> 34
29	Apex of floral scale emarginate, cuspidate	> 30
29	Apex of floral scales acute or obtuse, emarginate, muticous, mucronate, mucronulate, or cuspidate	> 31
30	Scale cusp 0.3(–0.5) mm; achenes 0.8–0.9 mm; anthers 0.3 mm; Arizona	Cyperus amabilis
30	Scale cusp 0.6–1.2 mm; achenes (0.5–)0.6 mm; anthers 0.1(–0.2) mm; se United States	Cyperus cuspidatus
31	Scale apex mucronulate or mucronate	> 32
31	Scale apex cuspidate	> 33
32	Spikelets 30–120 per head; floral scales 0.6–0.8 mm; styles 0. 1 mm	Cyperus difformis
32	Spikelets 3–12 per head; floral scales 0.9–1.1 mm; styles 0.3–0.4 mm	Cyperus fuscus
33	Achenes 0.7–0.8(–1.1) mm; cusp excurved; stamen 1; floral scales laterally strongly 3–4-ribbed	Cyperus squarrosus
33	Achenes 1–1.5 mm; cusp straight; stamens 3; floral scales laterally weakly 1–2-ribbed	Cyperus compressus
34	Inflorescences unbranched; achene apex emarginate; California	Cyperus gracilis
34	Inflorescences branched or unbranched; achene apex not emarginate; widespread	> 35
35	Floral scales laterally milky white (infrequently pale greenish white, brownish or bronzy white), laterally ribless; culms 0.4–1 mm wide; rays absent, inflorescence capitate; sw United States mountains	Cyperus seslerioides
35	Floral scales laterally light to dark reddish brown or stramineous, laterally 1–5-ribbed; culms (0.4–)1–4 mm wide; rays present or absent; inflorescences usually not capitate; widespread	> 36
36	Achenes with granular to papillose surface; inflorescence with 2d order (and 3d order) rays; leaves often without blades	> 37
36	Achenes with smooth, puncticulate, or papillose surface; inflorescence usually with primary (rarely 2d order) rays; leaf blades present	> 38
37	Rays 5–15; anthers 0.3–0.5 mm	Cyperus haspan
37	Rays 100–250; anthers 1–1.2 mm	Cyperus prolifer
38	Rachilla with wings 0.6 mm wide	> 39
38	Rachilla wingless or with narrow wings 0.1–0.2 mm wide	> 40
39	Spikelets compressed; achenes ellipsoid; inflorescence bracts 3–8; New Hampshire to Georgia	Cyperus grayi
39	Spikelets terete; achenes obovoid; inflorescence bracts 2–3; Florida	Cyperus filiformis
40	Longest bract ± erect	> 41
40	Longest bract oblique, horizontal or reflexed	> 43
41	Floral scales laterally 1-ribbed; achenes 0.7–0.8 mm	Cyperus onerosus
41	Floral scales laterally 2–4-ribbed; achenes 1.4–2.4 mm	> 42
42	Achenes broadly ellipsoid; floral scale apex with cusp 0.3–1 mm (in distal scales)	Cyperus schweinitzii
42	Achenes ovoid to obovoid; floral scale apex with mucro 0.1–0.3 m	Cyperus sphaerolepis
43	Plants with slender stolons, growing in wet soil	> 44
43	Plants with cormose bases, short, fibrous rhizomes, growing in dry soils	> 45
44	Floral scales ovate-elliptic, 20–60; spikelets not proliferous; Louisiana to North Carolina	Cyperus lecontei
44	Floral scales ovate, 3–20(–50); spikelets often proliferous; New Brunswick to South Carolina, Indiana	Cyperus dentatus
45	Longest bract oblique	> 46
45	Longest bract horizontal to reflexed	> 47
46	Apex of floral scale without mucro; achenes 2–2.4 mm; anthers 1–1.2 mm	Cyperus grayoides
46	Apex of floral scale with mucro 0.1–0.2 mm; achenes 1.5–2 mm; anthers 0.5–0.7 mm	Cyperus houghtonii
47	Floral scales reddish; rachilla wings 0.2 mm wide; Florida Keys	Cyperus fuligineus
47	Floral scales light brown, off-white, or stramineous; rachilla wingless; widespread	> 48
48	Anthers 0.8–1 mm; achenes 0.5–0.8 mm wide; floral scales yellowish; se United States	Cyperus filiculmis
48	Anthers 0.3–0.6 mm; achenes 0.8–1.2 mm wide; floral scales off-white to light reddish brown; widespread	Cyperus lupulinus
49	Rachilla articulate at base of each scale, mature spikelet disarticulating into segments, each consisting of scale, internode, and rachilla wings	> 50
49	Rachilla not articulate, or articulate only at base	> 51
50	Plants annual or short-lived perennial; spikelets (10–)20–60(–100) per spike; rays frequently present; achenes narrowly ellipsoid to oblong, (1–)1.2–1.5(–1.9) mm; widespread	Cyperus odoratus
50	Plants perennial; spikelets 2–8; rays usually absent; achenes obovoid, 2 mm; Florida	Cyperus filiformis
51	Floral scales with straight, excurved mucronate, or cuspidate apex 0.1–1.3 mm (basal scales often mucronate, with apex to 0.2 mm)	> 52
51	Floral scales entire or emarginate, with mucronulate apex at most 0.3 mm	> 60
52	Floral scales persistent, appressed, 3 or more mm; spikelets subcylindric; rachilla winged	> 53
52	Floral scales deciduous, spreading, usually less than 3 mm; spikelets quadrangular; rachilla wingless or wings at most 0.4 mm	> 55
53	Spikelets (4–)6–8(–14)-flowered, (8–)12–15(–24) mm; floral scales golden brown, stramineous, or hyaline; terminal scale conduplicate; Florida, Texas	Cyperus lentiginosus
53	Spikelets 1–3(–5)-flowered, 4–10 mm; floral scales green or hyaline, stramineous, or reddish; terminal sterile scale involute, frequently excurved; Mississippi to Arizona	> 54
54	Longest spikelets (2.2–)4–10(–18) mm; distal floral scales with glabrous midrib and mucro 0.1–0.3(–0.5) mm; anthers (0.3–)0.4–0.6 mm	Cyperus retroflexus
54	Longest spikelets 9–21 mm; distal floral scales with scabrid midrib and mucro 0.6–1.9 mm; anthers 0.5–1.3 mm	Cyperus floribundus
55	Plants perennial, not cespitose; rhizomes indurate, to 4 cm; floral scales weakly 3–7(–9)-ribbed, mostly medially	> 56
55	Plants annual (C. oxylepis perennial), cespitose with fibrous roots; rhizomes absent; floral scales 5–13-ribbed (C. oxylepis 2–3-ribbed) nearly to margins	> 57
56	Floral scales ovate-lanceolate, dull white, stramineous, or reddish brown; achenes 1.4–1.6 mm; anthers 0.4–0.9 mm; Arizona, New Mexico	Cyperus dipsaceus
56	Floral scales broadly ovate to oblong-ovate, stramineous or dull whitish; achenes 2–2.4 mm; anthers 0.8–1.4 mm; widespread	Cyperus schweinitzii
57	Floral scales strongly ribbed, (0.5–)1–2 mm wide; achenes 0.6 mm or less wide; stamens 1(–2)	> 58
57	Floral scales weakly ribbed, 1.5–3.6 mm wide; achenes 0.9–1.4 mm wide (0.5–0.8 mm wide in C. oxylepis); stamens 3	> 59
58	Floral scales 0.5–1 mm wide, (5–)7–9(–11)-ribbed; filaments 1.5 mm; anthers 0.2–0.3 mm; widespread	Cyperus squarrosus
58	Floral scales 1–2 mm wide, 5–13-ribbed; filaments 1.5 mm; anthers 0.8–1 mm; se United States	Cyperus granitophilus
59	Achenes obovoid, base cuneate to stipitate, not spongy, apex obtuse to emarginate; leaves flat to V-shaped, margins not involute; plants nonviscous when living	Cyperus compressus
59	Achenes ellipsoid, base stipitate, spongy, apex acute with beak 0.5–1.2 mm; leaves not flat to V-shaped, margins involute; plants viscous when living	Cyperus oxylepis
60	Spikelets linear, 0.8–1.9 mm wide; apex of scale barely reaching or as much as 0.4 mm from base of next scale	> 61
60	Spikelets oblong-ovate to linear-oblong, (0.5–)2–3(–4.5) mm wide; apex of scale equaling or surpassing base of next scale	> 62
61	Rachilla with hyaline or bronze, carmine, or yellowish thickened wings clasping achene; widespread	Cyperus odoratus
61	Rachilla wingless or with narrow, hyaline wings not clasping achene; Florida, North Carolina	Cyperus distans
62	Floral scales spreading or appressed (at least proximal portions of spikelet); spikelets compressed (2 or more times wide as thick)	> 63
62	Floral scales appressed; spikelets quadrangular to subterete (1–1.5 times as wide as thick)	> 88
63	Floral scales obovate-orbiculate, apex emarginate; styles less than 0.1 mm	> 64
63	Floral scales elliptic, oblong, or ovate, apex acute to obtuse; styles 0.2–3.6 mm	> 65
64	Spikelets ascending-appressed; rachilla with successive floral scales 0.7–0.9 mm apart (on same side of rachilla); scale apex with mucro 0.05–0.12 mm	Cyperus iria
64	Spikelets spreading; rachilla with successive floral scales 1.1–1.5 mm apart; scale apex with mucro 0.2–0.25 mm	Cyperus microiria
65	Rachilla with hyaline, whitish, or stramineous wings 0.2–0.6(–1) mm wide	> 66
65	Rachilla wingless or with wings less than 0.2 mm wide	> 76
66	Culms terete (at least in basal 2/3), nodose-septate when dried; inflorescence bracts 2(–4), erect; leaf usually reduced to sheath	Cyperus articulatus
66	Culms trigonous, not nodose-septate; inflorescence bracts 2–8, ± horizontal to ascending at 45° to reflexed; leaf blades present	> 67
67	Floral scales persistent; rachilla persistent; elongate stolons to 15 cm, bearing tubers	> 68
67	Floral scales deciduous; rachilla deciduous or persistent; rhizomes 0–5 cm, tubers absent	> 69
68	Floral scales yellowish brown to dark brown; base of culm soft stolons spongy, flexible when dried	Cyperus esculentus
68	Floral scales purple to reddish brown, with green midrib; base of culm indurate; stolons indurate, wiry, springy when dried	Cyperus rotundus
69	Culms 50–300 cm; 2d order rays 1–10 cm, distinctly flattened; 3d order rays 0.5–3 cm; coastal Louisiana	Cyperus prolixus
69	Culms to 100 cm; 2d order rays absent or less than 5 cm, terete to trigonous; 3d order rays absent; widespread	> 70
70	Culms trigonous, angles scabrid; Arizona	Cyperus hypopitys
70	Culms trigonous, glabrous or with a few prickles subapically; widespread	> 71
71	Achenes coarsely punctate; beaches, Florida, Georgia	Cyperus planifolius
71	Achenes glabrous or puncticulate; widespread	> 72
72	Base of culm swollen, cormlike	> 73
72	Base of culm not swollen	> 74
73	Floral scales 3.2–4.5(–6) mm; stigmas 3–4 mm	Cyperus strigosus
73	Floral scales 2–2.8 mm; stigmas 1–2 mm	Cyperus grayi
74	Rhizomes present; achenes 0.4–0.5 mm wide; anthers 1.5–2 mm; Great Plains	Cyperus setigerus
74	Rhizomes absent; achenes 0.6–0.9 mm wide; anthers 0.3–0.6 mm; sw, se United States	> 75
75	Achenes broadly ellipsoid; anthers 0.3–0.4 mm; floral scales red, reddish purple, or reddish brown; sw United States	Cyperus parishii
75	Achenes narrowly ellipsoid; anthers 0.6 mm; floral scales greenish white, often reddish brown speckled; Florida	Cyperus sphacelatus
76	Leaf blades involute; plants viscous when living	Cyperus elegans
76	Leaf blades flat or V-shaped; plants not viscous	> 77
77	Longest inflorescence bract ± erect	> 78
77	Longest inflorescence bract oblique, horizontal, or reflexed	> 79
78	Floral scales broadly ovate to oblong-ovate, apex with cusp 0.3–1 mm; achenes 2–2.4 mm; widespread	Cyperus schweinitzii
78	Floral scales ovate-deltate to orbiculate, apex with cusp 0.1–0.3 mm; achenes 1.4–1.6(–1.9) mm; Arizona, New Mexico, Texas	Cyperus sphaerolepis
79	Longest inflorescence bract ± horizontal to reflexed	> 80
79	Longest inflorescence bract oblique, ascending, or horizontal	> 83
80	Spikes cylindric	Cyperus fendlerianus
80	Spikes ovoid (hemispheric in C. fuligineus)	> 81
81	Floral scales reddish brown, 1.5–2.2 mm; Florida Keys	Cyperus fuligineus
81	Floral scales light brown to yellow, 2.5–4 mm; widespread	> 82
82	Anthers 0.8–1 mm; achenes 0.5–0.8 mm wide; floral scales yellowish to yellowish brown; se United States	Cyperus filiculmis
82	Anthers 0.3–0.6 mm; achenes 0.8–1.2 mm wide; floral scales off-white to light reddish brown; widespread	Cyperus lupulinus
83	Floral scales strongly ribbed laterally	> 84
83	Floral scales weakly ribbed laterally or ribless	> 85
84	Rachis hispidulous; achenes 1–1.2 mm; spikes loosely oblong-ovoid; wetlands, se United States	Cyperus pilosus
84	Rachis glabrous; achenes 1.5–2 mm; spikes subglobose to broadly ovoid; uplands, ne, Great Lakes region	Cyperus houghtonii
85	Culms glabrous or nearly so	> 86
85	Culms scabrid or scabridulous	> 87
86	Rachis 10–20 mm; anthers 0.4–0.6 mm	Cyperus spectabilis
86	Rachis 2–6 mm; anthers 1–1.2 mm	Cyperus grayoides
87	Floral scales (1.5–)1.8–2.4(–2.7) mm; achenes 1.3–1.8(–2.2) mm	Cyperus manimae
87	Floral scales 2.5–3 mm; achenes 0.5–0.6 mm wide	Cyperus cephalanthus
88	Floral scales deciduous; rachilla persistent, rachilla wings deciduous along lateral edge, base remaining firmly attached even after achenes fall; 2d order rays frequently present; spikelets with (6–)12–20(–40) floral scales	> 89
88	Floral scales persistent; rachilla deciduous (mature spikelets falling as unit from rachis) or persistent, rachilla wings persistent; 2d order rays absent or present; spikelets with (1–)2–5 floral scales	> 92
89	Culms leafless, (55–)200–350(–500) cm; inflorescences to 80 cm; 2d order rays to 20 cm; anther connectives subulate, 0.2–0.5 mm	> 90
89	Culms leafy, (5–)50–150 cm; inflorescences (2.5–)20–40(–50) cm; 2d order rays absent or at most 5 cm; anther connectives blunt, at most 0.1 mm	> 91
90	Rays slender, drooping or arching; inflorescence bracts 3–8 cm	Cyperus papyrus
90	Rays stiff, ascending to erect; inflorescence bracts (8–)20–45 cm	Cyperus giganteus
91	Plants annual; culms typically less than 25 cm × 1–2.5 mm; floral scales 1.3–1.5 mm; achenes 0.4–0.6 mm; anthers 0.2–0.3 mm; widespread	Cyperus erythrorhizos
91	Plants perennial; culms 50–150 cm × 2–15 mm; floral scales 1.6–1.8 mm; achenes 0.9 mm; anthers 0.4–0.5 mm; Florida, Texas	Cyperus digitatus
92	Spikes obtrulloid, obdeltoid to oblong-cylindric; spikelets, including distal, spreading to declined	> 93
92	Spikes cylindric, ellipsoid to obovoid, or globose; distal spikelets spreading or ascending, not declined	> 95
93	Culms glabrous; leaves and bracts glabrous except for marginal prickles; spikes ± 2 times long as wide; rachilla wing clasping achene for its entire length (therefore achene not visible in abaxial view); floral scales golden brown	Cyperus hystricinus
93	Culms (at least distal portions) densely scabridulous; leaves and bracts harshly scabrid or hirtellous on adaxial surface; spikes nearly as wide as long; rachilla wing clasping achene 3/4 or less of its length; floral scales grayish green to brown, often red-purple striate	> 94
94	Spikes loose, obtrulloid to obdeltoid; terminal scale not spinose; spikelets with 3–6(–8) floral scales; rays glabrous (rarely with a few antrorse hairs just proximal to spike); leaves and bracts with pubescence confined to midrib on abaxial side; rachilla wing papery with narrow, hyaline border, clasping achene for 3/4 its length; longest ray shorter than bracts; culm sharply angled	Cyperus retrofractus
94	Spikes tight, burlike, turbinate; terminal scale spinose; spikelets with 1(–2) floral scales; rays scabrid; leaves and bracts usually puberulent; rachilla wing hyaline, clasping achene ca. 1/2 its length; longest bract equaling or shorter than longest ray; culm obtusely trigonous to subterete	Cyperus plukenetii
95	Spikes densely cylindric (2–5 times longer than wide)	> 96
95	Spikes loosely to densely ovoid (1–2 times long as wide) or globose	> 104
96	Culms hispidulous on faces and angles distally, especially proximal to bracts; rays and rachis hispidulous; s Arizona	Cyperus dentoniae
96	Culms glabrous or occasionally with few prickles on angles only; rays and rachis glabrous; Florida or widespread	> 97
97	Culms, rays, and leaf blades papillose; leaves harshly scabrid on margins and midribs; Florida	Cyperus ligularis
97	Culms, rays, and leaf blades not papillose; leaves scabridulous or glabrous on margins and midribs; widespread	> 98
98	Spikelets oblong, lanceoloid, or cylindric, 4–10 times as long as wide, 3–8 fertile floral scales; spikes 7–40 mm wide	> 99
98	Spikelets ellipsoid to subulate, 2–4 times long as wide, 1–2(–5) fertile floral scales; spikes 5–11 mm wide	> 101
99	Floral scales greenish or light brown, apices overlapping proximal 1/4–1/3 of next scale; spikes ovoid to oblong-cylindric	Cyperus strigosus
99	Floral scales light brown to reddish brown, apices barely reaching base of next scale; spikes cylindric	> 100
100	Achenes narrowly oblong; floral scales light brown, bronze, or tawny; Gulf Coastal Plain	Cyperus thyrsiflorus
100	Achenes ellipsoid; floral scales pale greenish white, or golden brown to deep brown, or reddish brown; mountains, Texas to Arizona	Cyperus hermaphroditus
101	Bracts horizontal to ascending or reflexed; achenes (1.5–)1.8–2.2 mm	> 102
101	Bracts ascending at ± 45°; achenes 1.5–1.8 mm	> 103
102	Bracts horizontal to slightly ascending; spikelets 3–5 mm; anthers 0.4–0.6 mm; widespread	Cyperus aggregatus
102	Bracts horizontal to strongly reflexed; spikelets 2.4–3.6 mm; anthers 0.6–0.8 mm; Arizona, New Mexico	Cyperus pallidicolor
103	Achenes 0.7–1 mm wide; spikelets oblong-ellipsoid; Arizona	Cyperus mutisii
103	Achenes 0.5 mm wide; spikelets narrowly ellipsoid to subulate; California	Cyperus regiomontanus, see C. aggregatus
104	Floral scales more than 3.5 mm; achenes more than 1.5 mm	> 105
104	Floral scales usually less than 4 mm; achenes usually less than 2 mm	> 108
105	Spikes densely globose or globose-ovoid	Cyperus echinatus
105	Spikes ellipsoid to obovoid to loosely cylindric or oblong	> 106
106	Spikelets subquadrangular, subulate, with long, narrow terminal scale; leaves and bracts 3–6 mm wide, glabrous except for scabridulous margins; rhizomes well developed, thick	Cyperus hystricinus
106	Spikelets subterete, acute without long, narrow terminal scale; leaves and bracts often more than 10 mm wide, adaxial surfaces scabridulous; rhizomes poorly developed, short, hardly visible between approximate cormose culm bases	> 107
107	Spikes loose, 13–74 spikelets, each with (2–)3–6 floral scales; floral scales stramineous, red-purple striate, 4.5–5.3 mm; achenes straight, 5–6 times long as wide, 2.6–3.2 × 0.5–0.6 mm; anthers 1–1.5 mm	Cyperus refractus
107	Spikes dense, 50–90 spikelets, each with 3–6(–8) floral scales; floral scales whitish green, often yellow tinted, 4–4.6 mm; achenes conspicuously falciform, 3–4 times long as wide, 2.2–2.6 × 0.6–0.7 mm; anthers 0.7–1 mm	Cyperus lancastriensis
108	Spikes with ± parallel sides, mostly more than 25 mm; spikelets ± quadrangular	> 109
108	Spikes with curved (convex) sides, mostly less than 20 mm; spikelets somewhat compressed	> 112
109	Spikelets narrowly ellipsoid, 1.5–2 mm wide	Cyperus tetragonus
109	Spikelets oblong to linear, 0.6–1.6 mm wide	> 110
110	Achenes ellipsoid, sessile or nearly so; stigmas 1–1.5 mm; Texas to Arizona	Cyperus hermaphroditus
110	Achenes narrowly oblong, stipitate, stipe 0.1–0.2 mm; stigmas (0.5–)2–3(–4) mm; Georgia to Texas	> 111
111	Culms 0.5–1 mm wide; spikelets loosely packed on rachis (7–9 per 5 mm); leaves 0.8–2.8(–3) mm wide	Cyperus thyrsiflorus
111	Culms 2–2.6 mm wide; spikelets densely packed on rachis (11–21 per 5 mm); leaves (3–)4–5.8 mm wide	Cyperus pseudothyrsiflorus
112	Floral scales ascending, 1.7–2.5(–3.5) mm; achenes oblong-fusiform; rachilla wing thin, deciduous, narrow, less than 0.5 mm wide, covering less than 1/2 achene face	> 113
112	Floral scales appressed, mostly greater than 2.5 mm (rarely as short as 1.8 mm in C. retrorsus); achenes abruptly constricted, not fusiform; rachilla wing persistent, (0.2–)0.5–0.8 mm wide, covering at least 1/2 achene face	> 114
113	Floral scales stramineous; anthers 0.3–0.5 mm; achenes 1.2–1.5 mm; se United States	Cyperus ovatus
113	Floral scales brick red; anthers (0.7–)1–1.5 mm; achenes 1.7–1.8 mm; coastal California	Cyperus owanii
114	Spikes dense or loose, ovoid; spikelets angular, with (1–)2–4(–6) floral scales; floral scales whitish with red speckles; foliage yellow-green	Cyperus croceus
114	Spikes dense, globose, oblong to oblong-cylindric; spikelets subterete (not angular), with 1–3(–5) floral scales; floral scales stramineous, brown, fuscous; foliage green	> 115
115	Spikes globose to globose-ovoid; spikelets (3.5–)4–7 mm; floral scales membranous, stramineous to brownish, often red-brown between ribs, 3.5–4.5 mm; achenes 1.5–2.3 mm; bracts ascending at 30(–45)°, adaxial surface scabridulous especially distally; plants single-stemmed or loosely cespitose	Cyperus echinatus
115	Spikes oblong-ovoid, often with small basal branches; spikelets 2.2–4(–4.5) mm; floral scales nearly leathery, brown to stramineous or fuscous and lustrous, 1.8–2.5 mm; achenes 1.2–1.7 mm; bracts ascending at (30–)45°, scabridulous along margins, adaxial surface glabrous; plants densely cespitose	Cyperus retrorsus